<!DOCTYPE html>
<html>
 <head>
   <title>计算器</title>
    <meta charset="utf-8" />
    <link rel="icon" href="favicon.ico">
   <meta name="viewport" content="width=device-width" />
 </head>

 <body>
    <input id="num1" />*<input id="num2" />
    <button onclick="jiSuan()">=</button>
    <input id="num3" />
<script>
 function jiSuan(){
 num3.value = num1.value*num2.value;
}
</script>
</body>
</html>